Tuesday, Aug 28, 2012 - 6:00 AMIn the Kingdom of Mustang, between Nepal and Tibet and long off-limits to outsiders, explorers and scientists climb into human-carved caves thousands of years old. This National Geographic Special made for public television, follows team members up sheer rock cliffs into the caves where they find 14th-century wall paintings, ancient human remains and a centuries-old hidden library of sacred texts.G